The present invention relates to technique for arranging a developing machine housing toner in plural different colors opposite to a photoconductor, repeating operation for transferring on paper and an intermediate transfer member every color after one color toner image is formed on the photoconductor and generating a color print by transferring color toner images in all colors in a multicolor image formation apparatus such as a color printer, particularly relates to a multicolor image formation apparatus and a multicolor image formation method for controlling timing for forming a color toner image on the photoconductor.
An image formation apparatus such as a color printer and a color copying machine is generally constituted by means for overlapping and transferring color toner images in plural colors on paper and means for fixing the paper on which the color toner images are overlapped using a fixing device and generating a color print.
For example, as an image formation apparatus disclosed in the Examined Japanese Patent Application Publication No. Sho 59-17416, an apparatus in which a rotating drum holding one photoconductor, plural developing machines and a transfer member for holding a transferred medium are combined is also often used. In such an image formation apparatus, an electrostatic latent image is transferred by rotating the transfer member once after the electrostatic latent image in a first color is formed on the photoconductor by substantially equalizing the diameters of the transfer member and the rotating drum and rotating them synchronously, operation for developing the transferred electrostatic latent image is repeated every color and an image is formed, preventing the misregistration of color.
In the Unexamined Japanese Patent Application Publication Nos. Hei 4-119372, Hei 7-325455 and others, an image formation apparatus wherein a belt photoconductor and a belt intermediate transfer member are arranged with them combined, operation for transferring a color toner image on the intermediate transfer member is repeated every color after one color toner image is formed on the belt photoconductor, all color toner images are transferred on paper and sent to a fixing device after all the color toner images are transferred on the intermediate transfer member with the color toner images overlapped is proposed. In such an image formation apparatus for generating a color toner image using the belt photoconductor, to prevent the misregistration of color from occurring when images in each color are transferred on the intermediate transfer member with them overlapped, a reference mark is set on the intermediate transfer member. Every time the intermediate transfer member is turned, the reference mark provided to the intermediate transfer member is detected and timing for writing the next image is set using the detection signal.
According to the above image formation method disclosed in the Examined Japanese Patent Application Publication No. Sho 59-17416, the large misregistration of color is not caused basically, however, the misregistration of a few tens .mu.m is caused every color because of the precision of a gear and others. Even if each color image is off by approximately a few tens .mu.m, no visual sense of incompatibility is caused as the whole image. However, there is a problem that if an inevitable defect of approximately 100 .mu.m caused in the manufacturing process of a photoconductor exists on the photoconductor, the original defect of approximately 100 .mu.m lines with it off, is printed as a defect of 200 to 300 .mu.m and visually becomes very remarkable.
In the above image formation method disclosed in the Unexamined Japanese Patent Application Publication Nos. Hei 4-119372 and No. Hei 7-325455, a reference mark is set on an intermediate transfer belt, the reference mark provided to the intermediate transfer belt is detected every time the intermediate transfer belt is turned and timing for writing the next image is set using the detection signal. Therefore, according to this method, a visual sense of incompatibility caused by the misregistration of color is also not caused as the whole image. However, if an inevitable defect of approximately 100 .mu.m caused in the manufacturing process of a photoconductor on the photoconductor exists, the defect is transferred with it off by a few mm every color, the defect of approximately 100 .mu.m appears every few mm in a normal color image and becomes very remarkable visually.
The reason why a defect appears and is remarkable visually is as follows: The peripheral length of a photoconductor and the peripheral length of an intermediate transfer member are set so that they are equal or either peripheral length is integral times as long as the other peripheral length to prevent the misregistration of color and simplify control. However, the intermediate transfer member is in the shape of a belt, the peripheral length cannot be fixed under low temperature and high temperature, it is also difficult to manufacture the belt without an error and an error of approximately a few mm for desired length cannot be actually avoided. Therefore, as disclosed in the Unexamined Japanese Patent Application Publication Nos. Hei 4-119372 and Hei 7-325455, an intermediate transfer member is timed to prevent the misregistration of color. As a result, the generation start position of an image on a photoconductor is off by a few mm and a defect on the photoconductor lines with it off.
Also, as disclosed in the Unexamined Japanese Patent Application Publication No. Hei 7-325455, an electrification characteristic and a toner image formation characteristic are generally not fixed, slight dispersion exists on the surface of a photoconductor and there is a problem that a position in which a toner image in each color is generated cannot be arbitrarily set when a full color print is generated. It is described in the above patent application that if a color print is generated, a position for writing an image in each color is required to be set to a fixed position on a photoconductor. As a result, a defect on the photoconductor is transferred with it off by a few mm.